U.S. immigration authorities launched a series of raids, traffic stops and checkpoints in at least half a dozen states across the country on Thursday and Friday, sweeping up an unknown number of undocumented immigrants, immigration lawyers and advocates said.

The raids, which appeared to target scores of undocumented immigrants, including those without criminal records, mark the first largescale episode of immigration enforcement inside the United States since President Trump's Jan. 26 order to crack down on the estimated 11 million immigrants living here illegally.

It also appeared to signal a departure from the Obama administration's prioritized immigration enforcement against criminals. Trump has pledged to deport up to 3 million undocumented immigrants with criminal records.

Word of the raids quickly circulated among immigrants, activists and on social media, creating such widespread panic in immigrant communities that a Department of Homeland Security spokesperson said the department had decided to take the unprecedented step of confirming some details of the raids while the raids were ongoing.

Gillian Christensen, a spokesperson for the Department of Homeland Security, which oversees Immigration and Customs Enforcement (ICE), confirmed that ICE agents this week had raided homes and workplaces in Atlanta, the Los Angeles area and two other cities that she declined to identify, as part of "routine" immigration enforcement actions.

But immigration activists said Friday that they had documented ICE raids of unusual intensity in the last 48 hours in Vista, Pomona and Compton, Calif.; Austin, Dallas and Pflugersville, Texas; Alexandria and Annandale, Va.; Charlotte and Burlington, N.C.; Plant City, Fla.; the Hudson Valley region of New York; and Wichita, Kan.

There were also reports of ICE checkpoints, targeting immigrants for random ID checks, in North Carolina and in Austin.

The Trump administration is facing a series of legal challenges to his recent executive orders to crack down on undocumented immigrants and cities that appear resistant to his immigration policies. The raids also come on the heels of a Thursday night decision by the Ninth Circuit Appeals Court to keep a hold on Trump's travel and immigration ban of refugees and the citizens of seven majority Muslim countries.

Some activists in Los Angeles and Austin suggested that the raids might be retaliation for those cities' so-called "sanctuary city" policies.

Federal immigration officials declined Friday to say how many people had been detained in the recent raids. A DHS official confirmed that while immigration agents were targeting criminals, they were also sweeping up non-criminals in the vicinity who were found to be lacking documentation.

"Big cities tend to have a lot of illegal immigrants," said one immigration official who was not authorized to speak publicly because of the sensitive nature of the operation. "They're going to a target-rich environment."

Meanwhile, immigration advocacy and legal aid groups said ICE had declined to give them any information about how many people had been taken into custody.

Advocates from United We Dream, the Center for Community Change and Make the Road said on a Friday conference call with reporters that they believed hundreds to have been detained, including undocumented immigrants who had no prior criminal record. They said some had been deported immediately.

"We cannot understate the level of panic and terror that is running through many immigrant communities," said Walter Barrientos of Make the Road in New York City.

ICE agents had raided homes and were "not just detaining individuals they are looking for ... but in fact, taking anyone else in the community, or in these homes who does not have immigration status at the moment, or who is not able to prove citizenship," Barrientos said.

In some cities, activists said that ICE had set up roadside or neighborhood checkpoints, where ICE agents, often in unmarked cars, appeared to be asking people at random for proof of citizenship or identification.

"We're trying to make sure that families who have been impacted are getting legal services as quickly as possible. We're trying to do some legal triage," said Bob Libal, the executive director of Grassroots Leadership, which provides assistance and advocacy work to immigrants in Austin. "It's chaotic," he said. The organization's hotline, he said, had been overwhelmed with calls.

Federal immigration officials, as well as activists, said that the majority of those detained were adult men.